In order to meter the amount of air to an internal combustion engine, a variable positionable throttle valve is situated within the induction passage of the engine. Historically, a mechanical link mechanism is provided to couple the throttle valve to an accelerator pedal in a manner to move the throttle valve in response to movement of the accelerator pedal. More recently, so called "fly-by-wire systems" have been proposed which totally eliminate mechanical linkage between the operator's accelerator pedal and the engine throttle valve, providing, in its place, a torque motor which operates to position a throttle valve shaft in response to an electrical operator demand signal. The torque motor is part of an electrical servo control system including potentiometers which convert the movement of the accelerator pedal and throttle valve into corresponding electric signals which are electrically processed to drive the torque motor and thereby move the throttle valve to a position corresponding to a new position of the accelerator pedal. Such servo control systems permit ready modification of the systems response characteristics. For example, the host vehicle operator's perceived "feel" could be altered as a function of engine speed or other input variables. Furthermore, a characteristic could be further modified by other performance or safety related override functions.
Such arrangements typically employ a motor and throttle valve as separate elements, wherein an output shaft of the motor is connected to a throttle valve through a coupling, and wherein the degree of opening of the throttle valve is modulated in accordance with rotational displacement of the output shaft of the motor. Such arrangements have not received wide commercial acceptance, however. The provision of structure between the motor and throttle body tends to proliferate part count and unit cost as well as requires a large space in the engine compartment of the host vehicle. Additionally, the use of separate motor/throttle valve structures raise the possibility of certain failure modes in which torque transmission from the output shaft fails to appropriately position the throttle valve shaft such as through binding and the like.
The application of such devices as a prime throttle control for internal combustion engine of an automobile requires a high degree of reliability and responsiveness to varying operator and system input signals. Accordingly, the motor must be sized to provide extremely fast response to input signal changes over a sustained period of time and in an extremely hostile environment including large temperature gradients, contamination and corrosive atmosphere. Although the motor must have substantial electromagnetic "muscle" to provide appropriate response time, the rotating element's mass must be held to a minimum to prevent inertial induced overshoot requiring damping or other response degrading add-ons to the design. The requirement for reliability also extends to the design of the control circuit which, in addition to providing suitable operating characteristics, must be able to identify and distinguish component failures/anomalies from a validly demanded response.
It will be apparent from a reading of the specification that the present invention may be advantageously utilized with various types of electrical loads for many different applications. However, the invention is especially useful when used in combination with a throttle body for controlling the air inlet passage to an internal combustion engine, and will be described in connection therewith.